Hypertext Help with LaTeX

\sqrt

\sqrt[root]{arg}

The \sqrt command produces the square root
(radical) symbol with the argument as radicand. The optional
argument, root, determines what root to produce, i.e. the
cube root of x+y would be typed as $\sqrt[3]{x+y}$.

The radical sign is variable size,
that is, it is made larger if the radicand is, for example, a
built-up fraction.